Optical properties of Mg-implanted GaN grown on free-standing substrates

In this work, unintentionally doped GaN thin films were successfully grown on (0001) c-, (11-20) a- and (10-10) m-plane GaN free-standing substrates using metal-organic chemical vapor deposition. Subsequently, Mg was introduced into the GaN thin films through ion implantation (I/I) to prepare Mg-doped GaN (GaN:Mg). Compared with the c-plane substrate, non-polar a- and m-plane substrates were found to effectively enhance the concentration of MgGa acceptors while reducing the concentration of nitrogen vacancy-related clusters in I/I GaN:Mg. The origins of the ultraviolet luminescence peak, green luminescence band and blue luminescence band were analyzed by photoluminescence (PL) spectra. Two acceptor energy levels of Mg in I/I GaN:Mg were calibrated by measuring low-temperature PL spectra in the range of 5 K to 50 K.